TCO and light trapping in silicon thin film solar cells

Müller, J.; Rech, Bernd; Špringer, J.; Vaněček, M.

doi:10.1016/j.solener.2004.03.015

Cited by 975 publications

(552 citation statements)

References 40 publications

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“…1, [4][5][6] In thin-film silicon solar cells that employ nanoscale textures and metallic rear reflectors, transparent conductive oxide (TCO) rear buffer layers suppress localized surface plasmons that are excited in the metal by the rough surfaces. [7][8][9][10] For alkaline-textured monocrystalline wafers with micrometer-sized pyramids, however, a different loss mechanism must be responsible for parasitic absorption in the metal. In optical simulations of planar Si/SiO 2 /Al structures, Campbell observed diminished internal reflectance both above and below the Si/SiO 2 critical angle for thin SiO 2 layers, revealing that evanescent as well as propagating modes may be absorbed in the metal.…”

Section: Introductionmentioning

confidence: 99%

Improving metal reflectors by suppressing surface plasmon polaritons: a priori calculation of the internal reflectance of a solar cell

2013

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Imperfect internal reflectance of near-bandgap light reduces the performance of all solar cells, and becomes increasingly detrimental as absorbers become thinner. We consider light incident on the silicon/dielectric/metal structure at the back of rear-passivated crystalline silicon solar cells with surface textures that are large enough for geometric optics. By calculating the absorbance in the metal as a function of the angle of incidence, we discover three results that are important for understanding and improving rear reflectors in many types of solar cells. First, significant parasitic absorption occurs in the metal layer in two cases: s-and p-polarized propagating modes (near-normal angles of incidence) when the dielectric thickness is adjusted to cause destructive interference of the reflected beams, and p-polarized evanescent modes (angles of incidence above the semiconductor/dielectric critical angle) that excite surface plasmon polaritons at the metal surface. Second, the latter loss dominates; a well-designed rear dielectric passivation layer must suppress the penetration of evanescent waves to the metal. Third, when used as an input in a simple analytical model, the average rear internal reflectance calculated by assuming a Lambertian angular distribution of light accurately predicts the total reflectance and absorbance of a solar cell. INTRODUCTIONThe current trend towards higher silicon solar cell efficiencies has brought rear-passivated designs-including PERC (passivated emitter and rear cell), 1 interdigitated back contact 2 and heterojunction 3 structures-to the forefront of both research and production. While the impetus for rear passivation is a reduction in surface recombination and a corresponding gain in open-circuit voltage (V oc ), the dielectric passivation layer (or transparent conductive oxide layer in silicon heterojunction cells) can be made to simultaneously serve an optical role, thus increasing short-circuit current density (J sc ) too. Several authors have observed that even high-conductivity metals like silver are poor reflectors on textured silicon solar cells, and that a dielectric buffer layer increases the rear internal reflectance of infrared (IR) light. 1,[4][5][6] In thin-film silicon solar cells that employ nanoscale textures and metallic rear reflectors, transparent conductive oxide (TCO) rear buffer layers suppress localized surface plasmons that are excited in the metal by the rough surfaces. 7-10 For alkaline-textured monocrystalline wafers with micrometer-sized pyramids, however, a different loss mechanism must be responsible for parasitic absorption in the metal. In optical simulations of planar Si/SiO 2 /Al structures, Campbell observed diminished internal reflectance both above and below the Si/SiO 2 critical angle for thin SiO 2 layers, revealing that evanescent as well as propagating modes may be absorbed in the metal. 4,5 In a recent

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Section: Introductionmentioning

confidence: 99%

Improving metal reflectors by suppressing surface plasmon polaritons: a priori calculation of the internal reflectance of a solar cell

2013

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“…The nanotexture of the imprinttextured PET films was replicated using a two-step nanoimprint lithography process. First, the inverse of the surface texture of a wet chemically etched ZnO:Al substrate prepared at high temperature (300 °C) [17] was transferred into a soft polymer mold via hot embossing. Second, the original texture was replicated into a spin coated resist on the flexible substrate via UV nanoimprint lithography.…”

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Nanoimprint texturing of transparent flexible substrates for improved light management in thin‐film solar cells

Wilken

Paetzold

Meier

et al. 2015

Physica Rapid Research Ltrs

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We present a nanoimprint based approach to achieve efficient light management for solar cells on low temperature transparent polymer films. These films are particularly low-priced, though sensitive to temperature, and therefore limiting the range of deposition temperatures of subsequent solar cell layers. By using nanoimprint technology, we successfully replicated optimized light trapping textures of etched high temperature ZnO:Al on a low temperature PET film without deterioration of optical properties of the substrate. The imprint-textured PET substrates show excellent light scattering properties and lead to significantly improved incoupling and trapping of light in the solar cell, resulting in a current density of 12.9 mA/cm(2), similar to that on a glass substrate. An overall efficiency of 6.9% was achieved for a flexible thin-film silicon solar cell on low cost PET substrate

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“…The formation of poly-Si films on transparent conductive oxides ͑TCOs͒, however, would be an appealing option, especially for the preparation of thin-film solar cells in superstrate configuration because they allow for a simple contacting scheme and light trapping. 8,9 In the case of cells based on a-Si: H or c-Si: H, ZnO:Al is a promising TCO material due to its high stability in hydrogen-rich plasmas. 10 Studies on the stability of ZnO:Al upon treatment at higher temperatures as used for the crystallization of Si have so far concentrated on annealing of thin films on glass under various conditions.…”

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Temperature stability of ZnO:Al film properties for poly-Si thin-film devices

Lee

Becker

Muske

et al. 2007

Applied Physics Letters

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The crystallization of thin silicon films at temperatures between 425 and 600°C was investigated on glass substrates coated with Al-doped zinc oxide (ZnO:Al). Bare ZnO:Al layers degrade at the crystallization temperatures used. A silicon layer on top, however, efficiently prevents deterioration. The resistivity was even found to drop from 4.3×10−4Ωcm for the as deposited ZnO:Al to 2.2×10−4Ωcm in the case of aluminium induced crystallization and to 3.4×10−4Ωcm for solid phase crystallization. The temperature-stable conductivity of ZnO:Al films coated with Si opens up appealing options for the production of polycrystalline silicon thin-film solar cells with transparent front contacts.

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TCO and light trapping in silicon thin film solar cells

Cited by 975 publications

References 40 publications

Improving metal reflectors by suppressing surface plasmon polaritons: a priori calculation of the internal reflectance of a solar cell

Improving metal reflectors by suppressing surface plasmon polaritons: a priori calculation of the internal reflectance of a solar cell

Nanoimprint texturing of transparent flexible substrates for improved light management in thin‐film solar cells

Temperature stability of ZnO:Al film properties for poly-Si thin-film devices

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